Conduits are employed in electrical installation in buildings, exterior walls of buildings and similar structures, and are typically identified as Electrical Metallic Tubing [EMT], Ridge Metal Conduit [RMC], Intermediate Metal Conduit [IMC] and Aluminum Ridged Conduit [AL RC] conduits. These conduits are available in two type, threaded and threadless. Such conduits are sold in various lengths, usually about 10 feet, and in the field the threadless types are cut to the desired length for installation in junctions boxes, connected end to end to achieve a longer conduit run or connected to elbows or the like.
To connect threadless conduits end to end, couplings are required and to connect such conduits to junction boxes, connectors are used. Such couplings and connectors can be purchased from various suppliers stocking such parts. Couplings and connectors for EMT, RMC, IMC and AL RC threadless conduits are illustrated for conduit sizes from ½ inch to 4 inches, up to 6 inches for some conduits, in the National Electrical Code Handbook which is published every three years.
Since it is difficult to put pipe threads on the ends of the conduits in the field, especially large size conduits (conduit sizes greater than an inch and a half) most installation conduits use threadless conduits and “threadless” couplings and connectors to join them to other conduits and/or junction boxes. For each of the conduits, EMT, RMC, IMC and AL RC, the specifications in the referenced handbook for threadless couplings and connectors for such conduits are:
“a) Threadless. Threadless couplings and connectors used with conduit shall be made tight. Where buried in masonry or concrete they shall be concrete tight. Where installed in wet locations they shall be the raintight type.”
Applicant, an electrical contractor, has tested the available threadless couplings and connectors available in the industry by closing off one end or a short piece of conduit joining another piece of conduit to it with a coupling and submerging the short piece of conduit and coupling in a pool of water. None of the commercially available couplings were raintight based on these tests; that is the short piece of conduit and coupling filled with water in a short period of time. A similar test was done with commercially available connectors and none were found to be raintight.
In part water ingress results from variations in the outside diameter of the conduits and variations in the inside diameter of the connectors or couplings, which in larger conduit size installations can result in gaps in the range of 0.060 inch (or more) between the conduit and the connector.
On hundreds of thousands of roofs on commercial buildings, exterior walls and in industrial plants EMT, RMC, IMC and AL RC conduits are installed with threadless couplings and/or connectors which are not raintight even though the specifications for these installations more often than not require that the threadless couplings or connectors used should be “listed” as raintight.
While rain water is essentially distilled water with few impurities, once it contacts a metal conduit it dissolves metal atoms, along with other impurities, and becomes more conductive when it enters the interior of such conduits through a coupling or connector which is not raintight. As such water passes through the interior of the conduit system, it may short out electrical circuits, switch gear and the like. Of course corrosion from the intrusion of the rain water compromises such installation still further. For these reasons engineers specify that raintight threadless coupling and connectors for such conduits be used in wet locations, such as the roofs and exteriors of buildings. The problem is that all commercially available connectors and couplings for conduits in wet locations are not raintight with few exceptions, see for example the connector/coupling with an exterior elastomer boot illustrated in U.S. Pat. No. 3,951,436. The connectors/couplings in '436 patent are generally unsatisfactory due the ultra violet (UV) degradation of the boot, after which water intrusion can be extensive. Moreover the exposed boot is subject to damage during installation which can lead to its failure, e.g., contact with the sharp end of a conduit being inserted or tools used for installing and mounting conduits. As a result it is not often used in installations, if at all. In addition, rubber covers have been employed over the ends of couplings and connectors which are slipped on ends of the these fittings after the conduits have been secured in the fitting having been previously placed on the conduit, see for example U.S. Pat. No. 6,106,031 illustrating plastic end caps and an O-ring which are placed between the conduit and the fitting to effect a seal without any radial compression of the O-ring. Such covers also may provide some temporary sealing if the aperture in the cover is of a lesser diameter than the outside diameter of the conduit but such a seal may be short lived due to UV degradation, mechanical displacements and/or mechanical damage. Another coupling/connector design is illustrated in U.S. Pat. No. 5,165,735 which uses a un-compressed sealing washer to assist in reducing water intrusion into such fittings. Due to the ability of the washer to shift in the fitting and damage to the washer when the sharp end of a conduit is inserted, it may or may not be raintight initially and/or may ultimately not provide a raintight connection.
An object of applicant's invention is to provide couplings and connectors (fittings) for electrical installations which are raintight.
A further object is to provide such couplings and connectors, which are superior to those currently available in the industry.
Still another object is to provide couplings and connectors which are economical to produce so that installations in wet locations can employ threadless raintight couplings and connectors without a significant increase in cost over similar non-raintight couplings and connectors now sold in the market place.
Another object of this invention is to provide improved raintight couplings and connectors which ensure a continuous and adequate electrical ground through these fittings.
One of the more important objects is the provision of a fitting, whether a coupling or a connector, that has a positive seal which is not subject to UV degradation.
Other objects and advantages will be apparent from the specification which follows and the drawings accompanying this application.